1. Field of Invention
The present invention relates generally to the field of network bandwidth utilization, and specifically in one aspect to using variable bit rate streams on the network in order to provide support for services over a content-based network such as a cable television network.
2. Description of Related Technology
One significant competitive challenge presently faced by network operators relates to managing and conserving bandwidth while maintaining sufficient signal quality to subscribers. This includes the reclamation of otherwise under-utilized or unused bandwidth such that the service and/or customer base can be expanded without significant modifications or build-outs of the underlying network infrastructure. For example, it is clearly desirable to expand the types and availability of “next-generation” network services, including high-definition (HD) broadcast, VOD, high-speed data, VoIP, Interactive TV (e.g., “eTV”), etc. over time, without the need for major capital expenditures or system modifications. Hence, network operators are increasingly focused on techniques for squeezing as much capacity out of their existing networks as possible.
The foregoing need for bandwidth optimization and reclamation is also applicable to so-called “switched” network architectures. These architectures generally distribute all of the available content provided by the network operator (e.g., MSO) to switches within the network; these switches are then used to selectively provide only those channels actually watched or requested by users to their hubs or nodes for delivery, thereby effectively deleting unwatched channels from the digital broadcast stream. A “deleted” channel is automatically switched back on when a subscriber subsequently selects it, with the switching and delivery transition being for all intents and purposes transparent to the subscriber. This approach has obvious benefits from the standpoint of bandwidth conservation.
In the exemplary switched broadcast network architecture, it is often necessary to fix a certain bandwidth of each acquired program stream. Digital program streams are acquired in the head end of the network and include various components, including: (i) a video portion, (ii) an audio portion, and (iii) a data portion. Each one of these components consumes a certain bandwidth that changes over time in a generally non-predicable manner. The requirement to fix the bandwidth per stream stems from the desire to maintain a substantially known or constant bit rate for purposes of allocation and reallocation of specific resource size increments. This allows, inter alia, for the insertion and removal of streams by, e.g., servers in broadcast switched digital architectures. For example, in a typical broadcast switched architecture (BSA) network, the total bandwidth allocated to a program stream (all components) in standard definition (SD) is “clamped” at 3.75 Mbps.
By clamping the rate at a fixed value, excess bandwidth will sometimes be allocated to streams which do not require the full amount of bandwidth. In the context of the foregoing example, such a program stream might only require 3.25 Mbps peak, but is none-the-less allocated 3.75 Mbps. This added bandwidth takes the folio typically of inserted “null” packets which are loaded into each variable program stream in order to achieve the “constant” rate (e.g., 3.75 Mbps). These null packets are typically inserted at the rate clamping processor. The constant bit rate (CBR) streams including the null data are examined, and the null packets identified and removed (e.g., at the hub site or other distribution node).
Also, the aforementioned “constant” bit rates must be chosen to envelope possible rate peaks in the program material to prevent deleterious artifacts, thereby requiring that the constant rate selected often be significantly higher that what is actually required at any given time.
However, since the rate at which null packets are packed into the variable streams before transport can change significantly, the prior art merely identifies and removes the null packets from the program streams (e.g., at the hub), and does not make any attempt to utilize the bandwidth vacated by removal of the null packets for transmission of additional data. Furthermore, since this vacated bandwidth varies as a function of time, it is unpredictable in terms of availability, and hence ostensibly is not suited to supporting a time-sensitive (e.g., real time) data stream such as streaming video or audio.
Various Prior art approaches to smoothing out the variability in bit streams in general are known. For example, U.S. Pat. No. 4,594,708 to Servel, et al. issued Jun. 10, 1986 entitled “Synchronization for a digital train intended for a correct framing of received information” discloses a digital train that is synchronized to correct the framing of received information. To this end, the transmitted digital train is timely structured into recurrent time intervals having a fixed length. The information to be transmitted is divided into blocks called packets, having the length of a time interval and comprising a field of data and a header used for identifying the packets. A digital transmission system with a TDM multiplex is divided into equal and recurrent time intervals, wherein the information is indexed by an associated explicit header, and wherein the absence of information in a time interval is indexed by a specific header which is not used elsewhere as a header. Null bits and bytes are utilized as part of the packetization process.
U.S. Pat. No. 6,047,007 to Munday, et al. issued Apr. 4, 2000 entitled “Transmission of data on multirate networks” discloses mobile radio units that communicate at a lower bit-rate than the conventional switching rate of a fixed network. Such calls are identified by mobile-to-mobile recognizers which identify characteristic bit streams and handle calls appropriately. An incoming mobile-to-mobile recognizer normally routes the call to a digital-to-A-law transcoder. An outgoing mobile-to-mobile recognizer normally routes calls to a high bit-rate digital-to-A-law transcoder. If a call is established between two mobile users the first mobile-to-mobile recognizer diverts the signal received to a bit stuffer which provides three null bits for every bit received over the air interface. The null bits may be random numbers, but preferably include a recognizable pattern which can be detected by the second mobile-to-mobile recognizer. By such “bit stuffing” a 64 kbit/s signal can be generated from a 16 kbit/s signal with minimal signal processing and without the need to transcode to A-law and back.
U.S. Pat. No. 6,807,528 to Truman, et al. issued Oct. 19, 2004 entitled “Adding data to a compressed data frame” discloses apparatus for use of otherwise wasted bits in a bit stream. Many low bit rate digital audio encoding systems, including Dolby Digital and MPEG-2 AAC generate data streams in which unused dummy, fill, stuffing, or null bits exist whenever the bit allocation function in the encoder does not utilize all available bits from a bit pool. In the invention, all or some of such wasted bits are used to carry information. This can be accomplished after an encoder generates a bitstream. The resulting bitstream is analyzed to identify the locations of some or all of the unused bits. Some or all of the identified unused bits are then replaced with information-carrying bits to embed information-carrying bits in locations formerly occupied by unused bits. Alternatively, instead of replacing some or all unused bits in the bitstream with information-carrying bits after encoding, a modified encoder may insert information-carrying bits in some or all of the unused bit positions during the encoding process.
U.S. Pat. No. 6,895,544 to Park, et al. issued May 17, 2005 entitled “Encoding method of multimedia data and encoding device therefore” discloses an encoding method for wireless transceiving of multimedia data including video data, and an encoding device therefor. The encoding method includes (a) generating a length field representing the number of bits of a payload, (b) generating an error correction code by performing error correction coding with respect to the length field, and (c) inserting the length field and the error correction code during radio link protocol (RLP) framing. The encoding method reduces overhead when multimedia data including video data is transmitted and received under the radio environment, and increases error robustness, thereby improving the quality of an image. The encoding method further includes a step of generating a null indication field indicating an existence of only null data, if only null data exists without information data. Preferably, the method further includes steps of performing RLP framing for a fixed-length RLP frame and inserting into the frame a series of fill bits having a constant binary value during the RLP framing to achieve byte alignment to complete the fixed length.
U.S. Pat. No. 6,924,847 to Choi, et al. issued Aug. 2, 2005 entitled “VSB reception system with enhanced signal detection for processing supplemental data” discloses a VSB reception system that includes a sequence generator for decoding a symbol corresponding to the supplemental data and generating a predefined sequence included in the supplemental data at VSB transmission system. The reception system also includes a modified legacy VSB receiver for processing the data received from the VSB transmission system in a reverse order of the VSB transmission system by using the sequence, and a demultiplexer for demultiplexing the data from the modified legacy VSB receiver into the MPEG data and the supplemental data. The VSB reception system also includes a supplemental data processor for processing the supplemental data segment from the demultiplexer in a reverse order of the transmission system, to obtain the supplemental data, thereby carrying out the slicer prediction, decoding, and symbol decision more accurately by using the predefined sequence, to improve a performance.
U.S. Patent Application Publication No. 20020101921 to Golin, published Aug. 1, 2002 entitled “Controlling a video-buffer-verifier buffer using an MPEG-like encoder” discloses control of possible overflow of a video buffer verifier (VBV) buffer employed in MPEG-like video encoders by controlling bits being drained from a video encoder buffer (eBuff). Specifically, a number of bits in the encoder buffer is determined when a last prior picture ends, or when it should end. This number of bits (maxBits) is the maximum number of bits to be read from the encoder buffer and written to the remote decoder before a prescribed time T(n). When maxBits has been read from the encoder buffer and written to the decoder, the writing of bits to the remote decoder is stopped until the process is reset. The disclosed encoder also pads the encoded bitstream with null bits under certain circumstances.
U.S. Patent Application Publication No. 20020147991 to Furlan, et al. published Oct. 10, 2002 entitled “Transmission of panoramic video via existing video infrastructure” discloses technology that allows an immersive video to be transmitted from a first site to a second site using standard television infrastructure. Each frame of the immersive video is packed into at least one standard television frame. The standard television frame is suitable for transmission using standard television infrastructure. Once the standard television frame is received at the second site, the immersive video frame is reconstructed. The reconstructed immersive video frame can then be transmitted, recorded, viewed, or used to generate a view for transmission or recording.
U.S. Patent Application Publication No. 20020156915 to Haggar, et al. published Oct. 24, 2002 entitled “Technique for efficient data transfer within a virtual network” discloses methods, systems, and computer program products for improving the efficiency of data transfer within interconnected components of a virtual network, and in particular components of a single physical computing device, where the components exchange data as if they were communicating over an actual communications network using networking protocols. Data packets to be sent from one component to another are buffered by next-hop address (and optionally by final destination address as well) to improve efficiency of packet delivery. In one embodiment, outbound packing buffers are logically divided into a plurality of frames, the frames being associated with network addresses. The packing operation comprises packing the outbound data packets into selected frames of selected ones of the outbound packing buffers when a header of the outbound data packet to be packed specifies a first network address and a second network address which correspond to the selected outbound packing buffer and the selected frame.
U.S. Patent Application Publication No. 20050010960 to Kitazawa, et al. published Jan. 13, 2005 entitled “Video data multiplexing device, video data multiplexing control method, encoded stream multiplexing device and method, and encoding device and method” discloses the transmission of data for statistical multiplexing which is required for control using statistical multiplexing. By utilizing private packets, respective encoding devices transmit encoding difficulties serving as the data for statistical multiplexing to a multiplexer via the same transmission channels as encoded video data and audio data are transmitted. The multiplexer conducts multiplexing processing on data supplied from the respective encoding devices at a first rate R1 larger than a transmission rate on a transmission channel of a subsequent stage, and outputs a transport stream (TSd) including the private packets to a statistical multiplexing computer. In addition, the multiplexer conducts multiplexing processing on data obtained by removing the private packets, at a second rate R2 which is equal to the transmission rate on the transmission channel of the subsequent stage, and outputs a transport stream (TSm) which does not include the private packets to the transmission channel of the subsequent stage.
U.S. Patent Application Publication No. 20050100076 to Gazdzinski, et al. published May 12, 2005 entitled “Adaptive holographic wideband communications apparatus and methods” discloses apparatus and methods for utilizing holographic waveforms for a variety of purposes including communication. In one exemplary embodiment, the holographic waveforms are transmitted over an RF bearer medium to provide, inter alia, covert and robust communications. Frame “packing” or stuffing is disclosed; a constant or variable frame size is generated, and the frames stuffed up to capacity before transform and subsequent transmission. One embodiment uses a constant frame size; this approach maintains a constant frame size and frame rate, thereby in effect generating a somewhat unchanging signal emission in both the time and frequency domains. Other schemes for frame stuffing or padding are disclosed, including constant overhead byte stuffing (COBS) and zero-bit stuffing. Where the source or input data rate is insufficient to stuff the bits, such as where a non-continuous data source is utilized, either the coding rate may be adjusted (such as via a coding rate control algorithm which calculates the required coding rate necessary to maintain proper frame stuffing), and/or the data buffered (such as in a FIFO or comparable mechanism). Additionally, “stuff data” can be spontaneously generated and inserted into the frame structure as necessary to avoid use of variable code rates or buffering.
U.S. Patent Application Publication No. 20050122999 to Scherzer, et al. published Jun. 9, 2005 entitled “System and method for interference mitigation for wireless communication” discloses systems and methods which provide interference mitigation by making alternative resources available within areas served by wireless communication links. Embodiments provide multiple channel availability in establishing wireless communication links to facilitate interference mitigation. A frame aggregator/de-aggregator unit provides packing and unpacking of frames. Accordingly, packed frames are passed between frame aggregator/de-aggregator unit and encoder/decoder If there is not enough data for the fixed size frame, additional null bits may be concatenated as needed according to one embodiment.
Despite the foregoing broad variety of techniques for frame and packet “stuffing”, no suitable approach or apparatus for use of the bandwidth created by removal of the null or stuffed bits from bit streams or data structures is disclosed in the prior art. In the particular context of a content-based network, this bandwidth is effectively wasted, thereby reducing the efficiency of the network as a whole.
Hence, there is a salient need for improved apparatus and methods for making effective use of variations in data or program stream bit rate, and the aforementioned vacated bandwidth. Such improved apparatus and methods would ideally be applicable over a wide range of variable bit rates produced by, e.g., interactive applications used by the subscribers, while maintaining high video and audio data quality. Such improved apparatus and methods would also be substantially implemented using existing network infrastructure, without the need for large-scale or costly modifications or additions thereto.